signet

A self-hosted MCP server for the Pebble Index 01 ring.

Press the ring, talk. The phone transcribes it and picks a tool. When it picks one of signet's, the request goes to your own server instead of someone else's cloud.

A signet is a ring you press to authorize things.

Status

Working and deployed. Four tools (capture, ask, schedule, do), SQLite with full text search, scoped tokens, web search, and a mobile admin portal. Runs in Docker behind a Cloudflare Tunnel, verified against the real protocol the Pebble app speaks.

Not built yet: Google Calendar, so schedule saves the request and says so rather than dropping it. Also no approval queue, so anything marked destructive refuses to run. The plan is in docs/03-implementation-plan.md.

Related MCP server: cortex

How it works

Four tools is the whole surface the phone sees, because a ~1B on-device model has to pick one and more choices make it worse. Behind them sits an unbounded set of internal capabilities.

• capture saves what you said. No model call, and it still works when everything else is off.

• ask searches your journal, falls back to the web, and answers in one or two sentences.

• schedule is a calendar stub for now.

• do is the catch-all. Rules run first, then a model classifies what is left.

Answers come back in the MCP response itself, which is what renders in the app feed and reaches the watch. Push notifications are a fallback for work too slow to answer inline, not the normal path.

Nothing you say is dropped. No API key, spent budget, provider down, unrecognised request, or unbuilt feature all end with the text in your journal and a plain answer saying so.

What we learned about the Pebble app

This is probably the useful part if you own an Index 01. The app lets you add your own MCP server, but there are no docs, and a few things will bite you. All of this was read out of coredevices/mobileapp and then verified against a running server.

The app speaks MCP 2025-06-18. It ships MCP Kotlin SDK 0.8.3, which tops out there. Current SDKs default to 2026-07-28, where the whole initialize handshake no longer exists. Both eras can be served from one endpoint. The Python SDK still supports the old handshake, so no shim is needed.

Return all your tools in one page. The client hits a literal TODO("Handle pagination") and throws if you send a nextCursor.

Serve single JSON responses, not SSE. Cloudflare Tunnel buffers SSE until the stream closes, so an SSE response is one the ring never receives. The Python SDK's Streamable HTTP transport frames POST responses as SSE by default, which passes every local test and then hangs behind the tunnel. Turn it off with json_response=True.

Auth is one header, used verbatim. No OAuth, no dynamic registration. You type a single Authorization value into the app, so it has to include the word Bearer. Cloudflare Access service tokens will not work, because they need two headers the app cannot send.

instructions from initialize gets injected into the on-device model's context. Free system prompt channel. Use it.

Results can render as native items in the app feed. Set _meta.coreSchema to the integer 1 and return structuredContent with both output and semanticResult. Both keys are required: the app reads them with getValue() and throws if either is missing. The discriminator is type, and unknown fields are rejected rather than ignored, so send exactly the fields the variant declares.

You get no session context. No user id, no device id, no history. Every call arrives cold, so the server has to keep its own state.

Run it

uv sync
export SIGNET_TOKEN=$(python -c "import secrets; print(secrets.token_urlsafe(48))")
uv run python -m signet

Then check it, including the parts the ring cares about:

uv run pytest
uv run python scripts/legacy_handshake.py http://127.0.0.1:8300 "$SIGNET_TOKEN"

legacy_handshake.py is stdlib only, so you can run it against a deployed server from any box with Python.

To point the phone at it, add an MCP server in the Pebble app with your URL ending in /mcp, streamable set to true, and the auth header Bearer <your token>.

Deploy

Docker Compose, one container, no database yet. See DEPLOY.md.

Docs

License

MIT